1. Field of the Invention
The present invention relates to semiconductor devices such as dynamic random-access memories (DRAM).
The present application claims priority on Japanese Patent Application No. 2008-19813, the content of which is incorporated herein by reference.
2. Description of Related Art
In semiconductor devices such as dynamic random-access memories (DRAM), consumed current values increase as internal frequencies of internal circuits composed of metal-oxide semiconductor (MOS) transistors,
For this reason, it is necessary for semiconductor devices to use a plurality of voltage generators having high current capacities, which in turn excessively consume currents in case of low current consumption modes, thus increasing total power consumption.
To cope with such a drawback, various technologies have been developed and disclosed in various documents such as Patent Document 1.                Patent Document 1: Japanese Unexamined Patent Application Publication No. S64-42850        
The semiconductor device as disclosed in Patent Document 1 has a plurality of voltage generators so as to detect the internal frequency thereof, wherein the number of voltage generators being driven is decreased when the internal frequency is low, while it is increased when the internal frequency is high, thus generating an appropriate amount of current in response to power consumption. This technology prevents unnecessarily high levels of current from being generated, thus achieving low power consumption in semiconductor devices.
The present inventor has recognized that the above semiconductor device requires detection circuitry and control circuitry for detecting plural operating frequencies so as to turn on and off the plurality of voltage generators. This increases the overall layout area, i.e. the chip size of the semiconductor device, thus pushing up the manufacturing cost.
In addition, the above semiconductor device suffers from a problem in that power consumption cannot be substantially reduced because of the consumption of current by the detection circuitry and control circuitry.